1. Field of the Invention
The invention relates to a process and apparatus for truncating tubes and particularly tubes made out of cardboard or of plastic material.
2. Description of Background and Relevant Material
A known tube truncation apparatus includes a mandrel which is mounted in a cantilever fashion on a frame. In such a case, at least the exterior surface of the mandrel is fixed in position, while at least one knife is provided adjacent to the free end of the mandrel.
To truncate a tube, the tube is placed on the mandrel. Typically the exterior diameter of the mandrel is approximately the same or slightly smaller than the interior diameter of the tube so that the tube can be easily slid thereover. The tube is then rotated while the knife, carried for example by a carriage, is activated perpendicularly to the tube to penetrate the wall of the tube and cut completely through the tube until the knife meets a counterpart or hard counterknife provided on the mandrel.
Although the mandrel is fixed, the mandrel includes, for example, a retractable, expandable portion, which may be motorized for rotation. In order to rotate the tube which has been placed on the mandrel, the expandable portion of the mandrel is first activated to expand into contact with the interior of the tube and grip it securely before the motor is energized to rotate the expandable portion and the tube around the stationary part of the mandrel. The expandable portion of the mandrel may be provided adjacent to the free end of the mandrel in the proximity of the hard counterportion, but typically is located more towards the opposite end of the mandrel.
To make it possible to cut truncated portions of desired length and to then remove the truncated sections, the truncating apparatus includes a slide in the form of a ring which is slideably mounted on the mandrel so that the slide can move along the length of the mandrel, in addition to an exterior retractable abutment which is also longitudinally adjustable. The adjustment of the abutment in a longitudinal direction makes it possible to determine the length between the knife and the abutment. After the adjustment of the abutment, the slide presses the tube against the abutment, for example, by means of a spring, so that a desired length of tube can be cut and then ejected by activating the ejector after the exterior abutment has been withdrawn and the expandable portion of the mandrel has been retracted.
In this type of truncation apparatus, however, the expandable portion continuously rotates and it is clear that after expansion of this portion the end edges of the tube rubs respectively on the exterior abutment and on the slide in such a way that the end edges may become partially damaged. Moreover, inasmuch as the expandable portion of the mandrel is positioned ahead of the knife with respect to the free end of the mandrel, it is necessary to have a length of the tube on the mandrel which at a minimum corresponds to the distance between the knife and the interior end of the expandable portion in order to cut the last section of tube. Typically, the total length of the tube to be cut which is placed on the mandrel is greater than the sum of the lengths of tube sections which are actually cut from the tube. The excess length is necessary to make up for an amount of waste which unavoidably results from the cutting procedure, for example which is lost as sawdust. Inasmuch as it is difficult to estimate precisely the exact amount of this type of waste, the length of the tube must also include extra length to insure that a sufficient length of tube remains on the mandrel for cutting the last section of tube to a desired length. Thus, after the final cut has been made to form the last section of tube, a short length of tube remains which falls off the mandrel as a piece of scrap so that a fresh tube can be placed on the mandrel to begin a new cutting procedure. As a practical matter, the extreme end edges of the tube placed on the mandrel to be cut are usually of better quality than the end edges of sections cut therefrom during the cutting operation. Unfortunately, one end edge of the piece of scrap is one of the original end edges of the tube. Consequently, conventional tube cutting procedures are extremely inefficient in being unable to cut a tube in such a way that both of the extreme end edges of the original are recovered in a desired length of tube. Even in the best cases where the amount of the tube on the mandrel which is wasted is reduced to a minimum, the length of tube to be cut which projects from the mandrel is nevertheless not held very securely by the rest of the tube to the mandrel so that the tubes are presented to the knife at an angle and are not cut squarely. Finally, the maximum length of a truncated portion is limited to the maximum distance between the exterior abutment and the knife.
As previously mentioned, it is advantageous to recover the original end edges of tubes to be cut into sections which are formed from a continuously formed tube because the end edges of such continuously formed tubes are of particularly good quality and/or are intended for subsequent treatment, such as notching, polishing, coloration, and snap-rivetting. This is similarly true for tubes to be truncated which have been subjected to a surface treatment adapted to harden the exterior surface which causes the cutting of the tube to become a more delicate operation than if a raw tube was being cut. In either case, the present invention is particularly suitable in resulting with two sections of tube, i.e. the first section and the last section of tube, which have been cut so as to retain one of the two original end edges of the tube placed on the mandrel. The process and apparatus of the present invention is advantageous in overcoming the shortcomings of prior art techniques as to the quality of the end edges of the tube section, particularly an end edge of the section cut from the last portion of the tube on the mandrel. In addition, the amounts of waste and scrap are reduced and it is possible to cut lengths of tube which approximate the length of tube placed on the mandrel.